Solid catalysts have been used in a variety of systems principally fixed bed and fluidized bed reactors for effecting various conversions. A prominent use of catalysts is in the catalytic cracking of hydrocarbon feeds of the petroleum industry. Another example of late is the use of aluminosilicate catalysts for use in the exothermic conversion of alcohols and their ethers to aromatics and higher hydrocarbons of the gasoline boiling point range.
Extensive effort has been devoted to the development of the aluminosilicate catalyst to improve the efficiency of the conversion and in dealing with the heat generated by the highly exothermic reaction. In an attempt to control the temperature of reaction, two-stage catalytic reactors have been devised as disclosed in U.S. Pat. Nos. 3,931,349; 3,928,483; and 4,058,576. These patents involve the use of diluents in controlling the temperature of the reaction and also the use of heat exchange medium as disclosed in U.S. Pat. No. 4,058,576 for controlling the temperature of the reaction within the range of 600.degree. K. to 830.degree. K. These systems have the significant drawback in that a dual-or triple-stage system of catalytic beds must be developed. Usually the first stage involves a condensation reaction using an acidic catalyst, followed by the use of crystalline aluminosilicate zeolite catalysts for converting the condensed products into the gasoline boiling point range constituents. These reactors involve recycle which can result in the increased production of aromatics, particularly durenes which can crystallise out of the gasoline mixture and cause problems in use.
Another approach in controlling the temperature of the reaction is to use a fluidized bed of the catalyst as disclosed in U.S. Pat. Nos. 4,046,825; 4,138,440; 4,197,418; and 4,251,484. By using a fluidized bed of the zeolite catalyst, in particular the ZSM-5 type, conversion of methanol to gasolines is accomplished. However, the highly exothermic reaction has to be controlled in a manner such as disclosed in the U.S. Pat. No. 4,138,440 where the reaction temperature is controlled by the heat of vaporization of the liquid methanol charged to the system. In U.S. Pat. No. 4,197,418 the use of a complex baffle system restricts the upflow reactant bubble growth to in turn control the mass transfer and the reactant conversion. In U.S. Pat. No. 4,251,484 the use of heat exchange tubes in the fluidized bed of the catalyst maintains a hydraulic diameter within the desired limits to control the reaction. These systems thereby complicate the fluidized bed approach and do not always ensure the control of temperature throughout the fluidized bed.
Fixed bed catalytic reactors are favoured compared to the more difficult to control fluidized bed reactors. However, on an industrial scale fixed bed reactors as used in exothermic catalytic conversions have the problem of developing "hot spots" in various regions of the fixed bed reactor. This phenomenon is known as parametric sensitivity where the chemical reactor is very sensitive to the changes of operating variables such as reactant inlet temperature and reactant inlet partial pressure. Complex temperature sensing systems are required in the industrial scale catalytic fixed bed reactors in order to avoid catalyst damage, safety hazards and poor process selectivities in preventing hot spots in the reactor. Although the use of fluidized beds generally overcomes this problem, the fluidized beds involve complex gas flow patterns and non-uniform solid residence time. This makes the prediction of industrial dense fluidized bed performance a difficult task and complicates their generalized application and scaleup for use in industry. Therefore the fixed bed system is generally favoured. However, in an industrial sense the normal approach as disclosed in the above-noted patents is a two-stage reactor system, for example as particularly applied to the conversion of methanol into gasoline boiling point constituents. The reactor operates on a 7 to 9 recycle ratio, operating at 30 atm. and a temperature in the range of 316.degree. to 450.degree. C. to control the heat evolved in an adiabatic fixed bed reactor. In this system a significant methanol bypass or aromatic products backmix is taking place as a consequence of the recycle which may affect selectivity and increase the undesirable durene fractions in the gasoline.
In an effort to improve upon the fixed bed catalytic reactor involving highly exothermic catalytic conversions, a reactor model was developed and reported by A. Soria Lopez, H. de Lasa, J. A. Porras, Chemical Engineering Science Vol. 36, p. 285 1981 concerning a reactor which demonstrated pseudoadiabatic properties. The reactor model as investigated and disclosed in that paper involves the co-current flow of coolant along the outside of a tube containing a fixed bed of particulate catalyst for the catalytic oxidation of orthoxylene. That reactor simulation based on a unidimensional model, first approximation that assumed that temperatures change only with the axial position, suggested that the use of a co-current flow of coolant within a certain range relative to a particular concentration of reactants avoided hot spots developing within the reactor tube.
According to this invention a multitubular catalytic reactor has been designed for particular use with exothermal catalytic reactions which overcomes the problems of the above prior systems. The system may be particularly adapted for use in the exothermic catalytic conversion of lower alcohols and their ethers to gasoline boiling point range constituents.
According to an aspect of the invention, a multitubular catalytic reactor for exothermic reactions of gasoline constituent forming reactants comprises a bundle of parallel tubes and a confined volume of catalysts within each of the tubes along their length. Each of the tubes is continuous along its length and independent of all other tubes. The tubes have effective reactive regions therein, all of essentially the same length, as defined by a consistent confined volume of catalyst in each of the tubes. The tube bundle has an inlet side and an outlet side. A reactant header is in communication with the inlet side of the tube bundle and a product header is in communication with the outlet side of the tube bundle. An inlet to the reactant header for introducing reactants into the tubes is provided, and an outlet for the product header for withdrawing products therefrom is also provided. Means defines a discrete channel along adjacent tubes of the bundle to provide thereby a plurality of channels through the bundle where each tube of the bundle is in contact with coolant flowing in one or more of the channels. The plurality of channels have an inlet side and an outlet side. Means is provided within the reactant header for isolating the flow of coolant through the reactant header into the inlet side of the plurality of channels. An upstream coolant header is provided outside of and adjacent the reactant header. The upstream coolant header has an inlet for introducing coolant to the individual channels via the coolant flow isolating means in the reactant header to provide coolant flow in the channels co-current with the flow of the reactants in the tubes. Means is provided within the product header for isolating flow of coolant through the product header as coolant emerges from the outlet side of the plurality of channels. A downstream coolant header is provided outside of and adjacent the product header. The downstream coolant header has an outlet for withdrawing coolant from the individual channels via the coolant flow of isolation means in the product header.